全文获取类型
收费全文 | 766599篇 |
免费 | 6345篇 |
国内免费 | 2080篇 |
专业分类
化学 | 377268篇 |
晶体学 | 11159篇 |
力学 | 39954篇 |
综合类 | 20篇 |
数学 | 110664篇 |
物理学 | 235959篇 |
出版年
2021年 | 6535篇 |
2020年 | 7008篇 |
2019年 | 7914篇 |
2018年 | 14137篇 |
2017年 | 14500篇 |
2016年 | 16877篇 |
2015年 | 8848篇 |
2014年 | 14236篇 |
2013年 | 33167篇 |
2012年 | 27397篇 |
2011年 | 36011篇 |
2010年 | 25766篇 |
2009年 | 25844篇 |
2008年 | 33053篇 |
2007年 | 34486篇 |
2006年 | 25861篇 |
2005年 | 25483篇 |
2004年 | 22575篇 |
2003年 | 20698篇 |
2002年 | 19735篇 |
2001年 | 21058篇 |
2000年 | 16217篇 |
1999年 | 12504篇 |
1998年 | 10655篇 |
1997年 | 10411篇 |
1996年 | 9878篇 |
1995年 | 8783篇 |
1994年 | 8718篇 |
1993年 | 8406篇 |
1992年 | 9007篇 |
1991年 | 9558篇 |
1990年 | 9119篇 |
1989年 | 8997篇 |
1988年 | 8624篇 |
1987年 | 8569篇 |
1986年 | 8183篇 |
1985年 | 10432篇 |
1984年 | 10860篇 |
1983年 | 9093篇 |
1982年 | 9383篇 |
1981年 | 8801篇 |
1980年 | 8500篇 |
1979年 | 9126篇 |
1978年 | 9365篇 |
1977年 | 9132篇 |
1976年 | 9086篇 |
1975年 | 8717篇 |
1974年 | 8551篇 |
1973年 | 8869篇 |
1972年 | 6349篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A firm's logistics cost, including shipping and inventory-carrying, is a substantial percentage of its sales. Nevertheless, typical inventory-control methods ignore or insufficiently represent the shipping cost. This paper describes a recursive algorithm that determines the reorder cycle-time that minimizes total logistics cost. It allows for a realistic accounting of shipping cost, which is modelled here as a function of shipping distance and weight. The algorithm uses a relaxation procedure to identify a suitable initial approximation to the optimal order cycle-time and then, through a series of recursive steps, moves to the optimal result. We demonstrate the algorithm with a single item, with a group of items that share a common order cycle, and with multi-items when item demands are random variables. Experience with this algorithm indicates that it converges to the optimal result in a very few steps. 相似文献
102.
In developing travel demand models it is generally assumed that the base-year data used in developing the parameters, as well as the forecasted data to be used as independent variables for the design year, are of acceptable quality. The purpose of this paper is to present the application of error propagation theory in assesing the predictive quality of one type of travel demand forecasting model (multinomial logit models) and to demonstrate how error considerations can be used as a tool for identifying the optimal model. The general conclusions of this study are that: (1) it is indeed possible to quantify errors in dependent variables in logit models as a consequence of errors in independent variables; and (2) error consideration can be used as a tool for identifying the optimal model from a set of candidate models. Further research is recommended to develop better insights into the phenomenon of error propagation so that the consideration of errors can be a factor in decisions on model selection. 相似文献
103.
A. A. Slavnov 《Theoretical and Mathematical Physics》1989,79(3):579-587
V. A. Steklov Mathematics Institute, USSR Academy of Sciences. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 79, No. 3, pp. 347–358, June, 1989. 相似文献
104.
A. M. Vinogradov 《Acta Appl Math》1989,15(1-2):3-21
The main notions and results which are necessary for finding higher symmetries and conservation laws for general systems of partial differential equations are given. These constitute the starting point for the subsequent papers of this volume. Some problems are also discussed. 相似文献
105.
106.
We establish soliton-like asymptotics for finite energy solutions to the Schrödinger equation coupled to a nonrelativistic classical particle. Any solution with initial state close to the solitary manifold converges to a sum of a travelling wave and an outgoing free wave. The convergence holds in global energy norm. The proof uses spectral theory and the symplectic projection onto the solitary manifold in the Hilbert phase space. 相似文献
107.
We demonstrate a method that permits to obtain generalized solutions for some quasilinear equations and systems of hyperbolic
type. The corresponding variational principle is constructed using the theory of equilibrium of a potential in an external
field.
Dedicated to the memory of B. M. Levitan
Supported by RFBR grants Nos. 05-01-00522 and NSh-1551.2003.1, by Program No. 1 of the Branch of Mathematics, Russian Academy
of Sciences, and by INTAS project No. 03-51-6637. 相似文献
108.
The tape stripping technique is an experimental method frequently used for reconstruction of the in-depth distribution of various topically administered substances within the horny layer of human skin, e.g., compounds contained in sunscreens. Titanium dioxide (TiO2) nanoparticles (25–200 nm in diameter) are one such compound. Optical techniques which apply blue light are found to be suitable for reconstruction. However, the presence of particles affects the light propagation within the skin and therefore causes incorrect determination of strip thickness, leading to an improper reconstructed distribution of nanoparticle concentration revealed from the experimental data. This study evaluates the errors emerging from the use of blue (400 nm) and NIR (800 nm) radiation and finds the use of longer wavelength light more advantageous. Particles of different diameters are considered, and it is revealed that the application of small particles (25–60 nm) results in the lowest rate of error. 相似文献
109.
110.